We are interested in understanding (1) how cells regulate their ability to adhere to one another, (2) how cell- cell adhesion complexes might also function to transduce signals that inform the cell about the state of adhesion, a process known as signal transduction, and (3) the relationship of these regulatory events to human skin disease. This application represents the competitive continuation for this grant, which is funded through June 2012. Study of the mechanism by which PV IgG induces loss of adhesion in target keratinocytes has enabled us to build a model of desmosome regulation and signaling in which PV IgG bind to desmoglein 3 on the keratinocyte cell membrane and initiate a series of biochemical events including phosphorylation of p38 mitogen activated protein kinase (p38MAPK, p38) and heat shock protein 27 (HSP27). Funding of this grant over the past 4 years has enabled us to further elucidate the mechanism by which pemphigus IgG induce loss of adhesion in target keratinocytes. We have identified additional regulatory components of this mechanism enabling us to build a more integrated model of pathogenesis. Events downstream of p38 activation include (i) EGFR activation/phosphorylation, (ii) endocytosis of dsg3, plakoglobin and EGFR into early endosomes, (iii) and HSP27 phosphorylation. This process culminates in the destabilization of desmosomes, retraction of keratin intermediate filaments and alterations to the actin cytoskeleton, which collectively contribute to the loss of cell-cell adhesion/acantholysis. Additionally, we have attempted to translate our observations from the laboratory to the clinic through a clinical trial designed to test the efficacy of a proprietary orl p38 inhibitor in patients with pemphigus vulgaris. We hypothesize that the signaling and intracellular biochemical changes induced by PV IgG are an exaggeration of normal physiology that provides insight into the regulation of desmosome mediated cell-cell adhesion. In this proposal, we outline our plan to (i) further elucidate the intracellular signaling processes and mechanism of pemphigus acantholysis, (ii) to extend our understanding of desmosome regulation by pemphigus IgG to other pathophysiologic processes by determining if and characterizing these desmosome signaling and regulatory processes in biological events involving transitions in desmosome adhesion, and (iii) test the hypothesis in vitro and in vivo if targeting multiple components of the pathway simultaneously with a combination of different drugs can inhibit acantholyis with the goal to minimize drug concentrations when used in combination and therefore minimize potential off-target effects and systemic toxicities compared to when these drugs are used individually. As such, a significant outcome of these studies will be to translate our observations into effective treatments for pemphigus.